1. Field of the Invention
The present invention is directed to a tricolor fluorescent lamp, and more particularly to a tricolor fluorescent lamp adaptable both for decorative illumination as well as for a picture element in a color picture display.
2. Description of the Prior Art
There has been proposed a tricolor fluorescent lamp for decorative illumination which comprises a single tubular envelop having electrodes at both longitudinal sealed end and having therein partitions which divide the inside space or discharge space into three circumferentially spaced sections, these sections being coated with respective fluorescent substances that emit different colors, for example, red, green and blue. An external magnet is cooperative with the lamp to deflect the discharge path between the electrodes into any one or two of the three sections so as to emit the corresponding primary color or colors in predominant proportions, making possible to produce any other color by adjusting the amount of deflection. Thus, the above lamp as a whole can present any desired colors which is most advantageous for decorative illumination, but it is not allowed by the above construction to provide a viewing surface on which all the three color emitting sections appears, which renders such lamp unapplicable to the use as a picture element for a color display.
While on the other hand, it is known that fluorescent lamps of special configuration may be utilized to form the picture element for the color display, particularly for a large scale one, in lieu of conventional colored incandescent lamps or cathode ray tubes, because of the fact that they require less amount of power consumption than the colored incandescent lamps as well as that they provides higher luminance brightness than the cathode ray tubes. There have been proposed a wide variety of fluorescent lamps of such special configuration as to be applicable to the color display. FIG. 1 shows, for example, one typical lamp 1 which comprises a phosphor-coated tubular envelop of convoluted tridimensional configuration that contains a pair of electrodes and an ionizable medium. For construction of the color display a multiplicity of the above fluorescent lamps are to be arranged in matrix so as to form each one picture element 2 by the combination of three lamps 1R, 1G and 1B having the envelops coated with respective phosphers emitting different colors, i.e., red, green and blue, as illustrated in FIG. 2. In this construction, however, the lamps 1R, 1G and 1B are required to be driven separately with each other, or by a corresponding number of the discharging circuits and therefore each one of the picture elements 2 requires three separate discharging circuits. Accordingly, the utilization of such fluorescent lamps for the color display renders the driving or discharging circuit complex and requires a large number of components which render the whole device unacceptably bulky. Further, in the above arrangement, each of three separately driven lamps is subject to continuous on and off operations for causing the one picture element to present a desired color reproduction and is therefore subject to repeated heating and cooling operations so as to be exposed to the fluctuation in the surrounding temperature. In view of that the hue and luminance brightness of such lamp depend largely upon the surrounding temperature, such fluctuation will be the serious cause for irregular color reproduction and is therefore should be avoided for clear color reproduction in the color display. In addition, each of said lamps subject to the above on and off operations will inevitably require during the course of varying the color to be emitted from the one picture element a certain starting time, although it is much shorter than that required with the incandescent lamp but is still longer than that with the cathode ray tube, thus preventing the color display system from having a higher response characteristics as near as the cathode ray tubes.